I saw the pic you are talking about, I just followed the edge straight back from front to rear with a new box cutter blade, a little light pass at a time, then deeper, just like with a scalpel. I left a little bit of an overhang so it had a little more stability to it. I used a stright edge to mark a line to follow and cut,cut,cut away!! I didnt take any pics while I did it though, but I will still check at home to see if I got any others..